If you’re running .NET 4 and Visual Studio 2010 Beta 1 on Windows Vista, and planning to upgrade to Windows 7, please note: it won’t survive an upgrade and leaves the .NET Framework in a unfixable state. Beta 2 isn’t affected, revealed Scott Hanselman. So, if you're running .NET 4 and Visual Studio 2010 Beta 1 on Vista you've got two options: 1. Uninstall Visual Studio 2010  and .NET Framework 4 Beta 1 and upgrade to Windows 7. Then reinstall .NET Framework 4 and Visual Studio 2010 Beta 1. Or 2. You can do a clean install of Windows 7, which’s recommended.